This invention relates generally to insulation sleeving, such as for providing thermal, electrical and/or mechanical protection, and more particularly, to insulation sleeving of the type comprising an inner sleeve of woven synthetic fiber and an outer coating of silicone elastomer particularly suited for providing thermal and electrical insulation for cables, cable connections and the like.
Insulation sleeving comprising a fiberglass braid inner sleeve and a coating of silicone elastomer is known. In the manufacture of such conventional insulation sleeving, a sleeve comprising a tubular braid of fiberglass yarn is initially prepared by means of a braiding machine. The tubular fiberglass braid or sleeve is then heat cleaned by subjecting it to a high temperature, to thereby singe or "heat shave" all of the fiberglass filaments which were broken during the braiding process. The fiberglass sleeve is then subjected to a caramelizing treatment carried out by passing the sleeve through an oven in which electrical resistors operate at high temperatures whereby the sizing of the fiberglass is eliminated to provide the sleeve with improved adhesion characteristics for the silicone elastomer coating to be applied. A coating of silicone elastomer is then applied over the surface of the tubular fiberglass braid. For example, in a continuous coating process, the braided fiberglass sleeve passes through an extruder head into which the silicone elastomer coating material is injected. Finally, the coated sleeve is passed through a curing oven operating at high temperatures where the silicone elastomer reticulates to thereby obtain the insulation sleeving.
Although conventional insulation sleevings provide excellent thermal and electrical insulation properties, as well as good mechanical protection in certain applications, there are certain limitations to which such sleevings are subject. For example, conventional insulation sleevings are substantially non-expansible in the radial direction, i.e., it is not possible to significantly increase the diameter of conventional insulation sleeving. For this reason, it is necessary for a manufacturer to produce and stock insulation sleevings having different diameters for different applications. For example, inventory must be maintained of insulation sleevings having about a 1.0 inch diameter for fitting 1.0 inch diameter cable, about a 1.5 inch diameter for fitting 1.5 inch diameter cable, about a 2.0 inch diameter for fitting 2.0 inch diameter cable, etc. This of course is costly and requires allocation of substantial capital to inventory.
Furthermore, conventional insulation sleeving cannot be used in applications that involve abrupt and considerable changes in cross section of the region to be insulated such, for example, as in the case of electrical connections. For such applications, it has been the practice to apply heat shrinkable tubings over the connections whereupon heat is applied to shrink the tubing onto the connection. However, the insulation provided by such that shrinkable tubings is less effective from the standpoint of mechanical protection, among others, than insulation sleeving formed of silicone elastomer-coated fiberglass braid due, among other things, to the omission of the fiberglass braid.